The present invention relates to a heat pressing apparatus that heat-presses a wood raw material together with an adhesive to produce a woody material, and relates to a method for producing the woody material, the wood raw material being an aggregate composed of a single plate, a sheet-like article in which fibers are opened by a rolling, a thin stick-like article, a flake-like article, a strand-like article, and the like. More particularly, the present invention relates to a technique for releasing steam, which stays in an interior of the wood raw material, to the outside when the material is heat-pressed, thereby to prevent a puncture caused by the steam.
Wood fibers or wood chips are added with a bonding material, and are formed into a woody material. The woody material is called a fiber board or a particle board, or may be collectively called a woody board. The woody material is produced by a heat-press forming process. In this process, the wood fibers or wood chips are added with the bonding material, such as phenolic resin adhesive, and are formed into a mat, and then the mat is pressed, while being heated to a temperature at which the bonding material is hardened. Heat pressing apparatuses have been widely used for such heat-press forming process.
The heat pressing apparatuses are designed to simultaneously heat and press the mat by heated surfaces of press platens.
When the wood raw material (mat) has a density of 0.4 g/cm3, the woody material (woody board) to be produced has a density greater than 0.4 g/cm3, and more specifically, greater than 0.7 g/cm3. Thus, the compressed wood raw material prevents the steam in the interior of the material from releasing to the outside. The steam therefore tends to stay in the interior of the material.
Then, this steam is abruptly discharged to the outside, when the press platens decompress the woody material. This causes a phenomenon or a rupture of the woody material or woody board. The phenomenon is called a puncture. The puncture occurs in the last phase of the woody board production process. Thus, the puncture spoils almost the whole production process. This leads to a substantial reduction in productivity, and therefore, involves an increase in production costs.
The aforementioned puncture phenomenon also occurs when the heat-pressing continues or when the wood raw material is heat-pressed under a high temperature and high pressure with its side surfaces shielded to obtain a woody material having excellent dimension stability.
It is thus crucial to prevent the puncture from occurring in the woody board production process. However, currently there is hardly any solution available to effectively preventing the puncture, except drying the wood raw material sufficiently before heat-pressed.
Another example technique for preventing the puncture is also disclosed: heat-pressing work is done in a vacuum space. However, this technique is not practical due to the need for a more complex system and the lower productivity.
Also, an enormous amount of energy must be needed to reduce water content of the wood raw material, to the extent that the puncture is prevented. This enormous amount of energy is used only for a step of drying the wood raw material, but not used for forming the woody material. In turn, the heated wood raw material must be cooled when the adhesive is coated on the material.
In the event that, in order to avoid wasting the enormous amount of energy, the wood raw material having high water content is coated with the adhesive without drying the material, and is subjected to forming and heat-pressing, a puncture would occur and preclude the production of the woody material. Therefore, it is desirable to prevent a puncture from occurring when the press platens heat-press and decompress the wood raw material, even if the wood raw material has high water content. This leads to skipping the drying step, and thus, achieves an energy-saving, space-saving production process.